1. Field of the Invention
The present invention relates to an ultraviolet-curable release agent composition, which due to the releasability of the cured film thereof, can be used as a treatment agent for the back surface of a pressure-sensitive adhesive tape, or as a coating material for a release sheet, such as a release paper, a release plastic film, or a release metal foil, for use with pressure-sensitive adhesive labels.
2. Description of the Prior Art
A variety of ultraviolet-curable silicone compositions have been proposed. In recent years, a multitude of curing methods have been proposed in which an epoxy group-containing silicone is cured using an onium salt photoinitiator as a catalyst (see patent references 1 to 3). This type of curing method is less susceptible to curing inhibition caused by oxygen than curing methods that utilize a radical reaction, and because the curing reaction proceeds favorably in air, these compositions are now being used as treatment agents for the back surface of pressure-sensitive adhesive tapes, and as coating materials for release sheets, such as release papers, release plastic films, or release metal foils, for use with pressure-sensitive adhesive labels.
For example, a packaging tape comprises a substrate tape and a pressure-sensitive adhesive coated on one side of the substrate tape, and further comprises a release coating on the opposite side of the substrate tape. The packaging tape is wound before use into a roll such that the pressure-sensitive adhesive coating comes into contact with the release coating. The packaging tape is unwound for use by peeling the pressure-sensitive adhesive layer side thereof off the release coating side. A minimum force required to peel the release coating from the pressure-sensitive adhesive layer is referred to as “release force”.
Furthermore, packaging tapes are widely used in automatic taping operations, and these automatic taping machines are designed to operate with tapes of uniform release force. If the value of this release force is small, then the fluctuation in the release force at the time of release is minimal, but if the release force is large, then the fluctuation in the release force tends to increase. If this fluctuation in the release force is too great, then the automatic taping machine, which has been designed on the premise of a uniform release force, may be unable to function normally. Furthermore, if this fluctuation in the release force is too great, then peeling noises tend to occur. Reducing such peeling noises is usually desirable in terms of maintaining a favorable working environment.
For the reasons outlined above, a release agent that exhibits a tight release force with minimal fluctuation in the release force upon peeling has been greatly sought.    [Patent Reference 1] GB 2 123 842 A    [Patent Reference 2] EP 0 391 162 A2    [Patent Reference 3] US 2003/0232900 A1